1. Field of the Invention
The present invention relates to the field of machine tools and more particularly to modifications with which a movable machining device can be displaced at high speed under the best environmental conditions.
2. Discussion of the Background
High-speed machining of parts in a machine tool generally takes place using a rotationally driven bit at the end of an electric spindle installed in a slide, which itself is mounted to be movable along two axes X, Y of a plane parallel to the plane of machining of the parts.
To facilitate reading of the description to follow, the plane XY of mobility of the movable device constituting the slide of the electric spindle will be assumed to be vertical, as is the case in the majority of embodiments of this type of machine tool in the field of high-speed machining.
A machine tool is classically provided with three main working stations, to wit:
a machining station proper, provided with the bit driven rotationally at the end of the electric spindle and shaping the part to be machined, PA1 a drive station situated upstream from the machining station and made up of an assembly of devices that ensure in particular the X, Y and Z displacements of the slide of the electric spindle and the rotation of said spindle, PA1 and a control station cooperating with the drive station and functioning with a program of instructions preestablished to take charge of the different stages of machining of the said part. PA1 the first, fixed relative to the frame, is provided with a window through which the said movable device passes and the inner edges of which define the limits of freedom of motion of the latter, PA1 the second, mounted slidingly relative to the first panel along the two displacement axes X, Y, has dimensions overlapping those of the window of the first panel and is provided with a window permitting motion of the said movable device, PA1 and the third, movable and with dimensions substantially larger than those of the window of the first panel, accommodates at its center the said movable device, in such a way that the displacements of the movable device in the window of the first panel in the plane of the two axes X and Y brings about proportional mobility of the intermediate second panel, which is suitable for filling the opening of the window of the first panel left uncovered by the third panel as it accompanies the displacements of the said movable device. PA1 the exterior panel can cover the part of the front face of the housing which is open around its window defining the limits of advance of the said movable device, PA1 the intermediate panel can fill in as cover for the opening of the window of the exterior panel left free around the interior panel when the said movable device is displaced inside the said window, especially when it is close to the edges thereof, PA1 and the interior panel can ensure that the opening of the window of the intermediate panel is covered around the said movable device.
The Applicant has observed that, in machine tools for high-speed machining, the separation of the machining station from the drive station is never physically well defined, especially as regards the virtual vertical plane marking the boundary between the two stations. In fact, to permit free motion of the movable slide along the two axes X and Y in a displacement plane parallel to this vertical boundary plane, the most classical embodiment comprises making the external machining zone communicate with the internal drive zone of the machine. This results in major problems of protection with respect to how closely personnel can approach the inside of the drive station and also to the devices of the drive station, which are sensitive to thrown-off machining chips and to pollution in the external environment of the machine, which is generally placed in the midst of a more or less contaminated atmosphere.
This separation becomes necessary when the motors driving the devices of the machine in translational movement are linear motors. In fact, these motors are equipped with a permanent-magnet block, which thus attracts all wastes of metallic nature. In addition, the leaktightness of such a structure, which is most often planar, is never perfect regardless of the means for assuring leaktightness.
The publication DE A 4405247 describes a physical element having the form of a protective cowling for a device movable along two axes in a plane, comprising elements disposed parallel to the plane of displacement of the said movable device and guided by at least two pantographs, the end points of which are joined in articulated manner to the fixed first element and to a movable element, and the intermediate points of which are joined to movable intermediate elements, such that a displacement of the movable last element brings about a proportional displacement of the intermediate elements. In the present case of machine tools for high-speed machining, this protective cowling is therefore supposed to permit the installation of a distinct boundary between the machining station and the drive station and, in addition to sealing functions, it must also ensure great freedom of motion of the movable device (slide carrying the electric spindle) in a plane parallel to the machining plane. This preliminary disposition of the protective cowling has as an advantage the ability to act dynamically as a "hermetic" seal for the housing enclosing the devices of the drive station while ensuring that the movable device extending from the said housing has the kinematic ability necessary for positioning the bit during the different machining phases. In addition, the guarantee of leaktightness of the housing to external pollution for protection of the sensitive devices assembled in the drive station can be further improved by pressurizing the internal volume thereof relative to the outside situated behind the protective cowling.